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Publication numberUS5482774 A
Publication typeGrant
Application numberUS 08/418,028
Publication dateJan 9, 1996
Filing dateApr 6, 1995
Priority dateNov 28, 1989
Fee statusPaid
Also published asUS5478647
Publication number08418028, 418028, US 5482774 A, US 5482774A, US-A-5482774, US5482774 A, US5482774A
InventorsKenichi Miyamoto, Haruyoshi Minamiguchi
Original AssigneeSumitomo Rubber Industries, Ltd.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Composite prepeg and tennis rackets using the same
US 5482774 A
Abstract
A composite prepreg for producing a tennis racket, which is light and tough and superior in flexibility and vibration absorption abilities, comprises thermosetting resin and reinforcing fibers, wherein the reinforcing fibers are a combination of (a) aromatic polyamide or polyester fibers and (b) carbon fibers, the fibers (a) being formed into a first type of strand and the fibers (b) being formed into a second type of strand, the first and second types of strand being arranged with certain regularity. The present invention is also directed to a tennis racket comprising a circular frame constituting a ball hitting area and a shaft connecting with the circular frame, the frame and shaft having a plurality of layers structured so that at least one layer is formed from the above described composite prepreg.
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Claims(3)
What is claimed is:
1. A tennis racket comprising a circular frame member constituting a ball hitting area and a shaft member connecting with said circular frame member, said frame and shaft members having a plurality of layers structured such that at least one layer is formed from a composite prepreg, said composite prepreg comprising a thermosetting resin and reinforcing fibers embedded therein, wherein said reinforcing fibers are a combination of (a) aromatic polyamide fibers, polyester fibers, or a mixture of aromatic polyamide fibers and polyester fibers and (b) carbon fibers, said fibers (a) are formed into a plurality of first yarn strands and said fibers (b) are formed into a plurality of second yarn strands, a ratio between a diameter of said second yarn strands and a diameter of said first yarn strand is in the range of 2 to 2/3, and said first yarn strands and said second yarn strands are arranged substantially in a plurality of sequential units of said first and second yarn strands therein.
2. The tennis racket according to claim 1 wherein said frame and shaft includes a core and five prepregs wound on said core.
3. The tennis racket according to claim 2 being prepared by winding said five prepregs around said core and then heating in a mold.
Description

This application is a divisional of copending application Ser. No. 08/338,216, filed on Nov. 4, 1994, now pending, of which is a File Wrapper Continuation of Ser. No. 07/618,607, filed Nov. 27, 1990, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a composite prepreg containing two reinforcing fibers and a tennis racket produced from the prepreg.

BACKGROUND OF THE INVENTION

A tennis shaft or frame is generally produced by winding one or more prepregs around a core material and then heating in a mold. The prepregs are composed of thermosetting resin and reinforcing fibers embedded therein. As the reinforcing fibers, carbon fibers and glass fibers have been employed for years. In order to improve strength, flexibility, impact resistance, feeling when hitting balls (i.e. vibration absorption etc.) and weight saving, aromatic amide fibers and aromatic polyester fibers are also proposed together with carbon and glass fibers in Japanese Kokai Publications 69870/1982, 142572/1987 and 141678/1989.

The aromatic amide and polyester fibers, however, are too tough and associated with problems in producibility in the case of being embedded as a sole layer. For example, in a drilling process for creating holes for passing gut through the frame of the racket, it is difficult to drill such holes due to the toughness of the aromatic amide or polyester fibers embedded in the tennis racket frame. Also, in a buffing process for smoothening surface, fuzzing often occurs. Furthermore, the inter laminated shear strength would be insufficient because of different physical properties among adjacent laminated layers.

SUMMARY OF THE INVENTION

The present invention provides a composite prepreg for producing a tennis racket which is light and tough and superior in flexibility and vibration absorption abilities. The composite prepreg of the present invention comprises thermosetting resin and reinforcing fibers embedded therein, wherein the reinforcing fibers are a combination of (a) aromatic polyamide or aromatic polyester fibers, or the both and (b) carbon fibers and the fibers (a) and (b) are arranged with certain regularity.

The present invention also provides a tennis racket comprising a circular frame constituting a ball hitting area and a shaft connecting with the circular frame, the frame and shaft having a plural layer structure in which at least one layer is formed from the above-mentioned composite prepreg.

The present invention will become more fully understood from the detailed description giving hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein:

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 schematically shows a section of the five prepregs layers;

FIG. 2 shows directions for pressing a tennis frame to determine frame strength;

FIG. 3 shows a system for determining vibration absorption; and

FIG. 4 schematically shows a process for preparing the composite prepreg of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The aromatic polyamide fibers employed in the present invention include aramide. Some of the polyamide fibers are commercially available under the trade names Kevler and Towaron. The aromatic polyester fibers include polyacrylates. They are commercially available under the trade names Vectran and Econol. In the present invention, the use of aromatic polyamide fibers or polyester fibers, or both (a) are combined with the carbon fibers (b), but the weight ratio of (a)/(b) is preferably within the range of 30/70 to 70/30, more preferably 40/60 to 50/50. Weight ratios of more than 70/30 do not impart sufficient toughness and those of less than 30/70 are poor in vibration absorption properties.

The fibers (a) and (b) are collected to form fiber strands which are embedded in the thermosetting resin. The carbon fiber strands preferably have a diameter of 1,800 to 7200 denier, more preferably 3,600 to 7,200 denier. The aromatic amide or polyester fiber strands preferably have a diameter of 1,500 to 7,500 denier, more preferably 4,500 to 7,500 denier. A diameter ratio between the carbon fiber strands (b)/the amide or polyester fiber strands (a) is preferably within the range of 2 to 2/3 in order to enhance the uniformity between the prepregs and to increase the adhesive ability between the layers.

According to the present invention, the strands of fibers (a) and the strands of fibers (b) are arranged with a certain regularity. The terminology "with certain regularity" is not understood strictly and certain regularity is seen to some extent as a whole. For example, the strands of fibers (a) and the strands of fiber (b) (hereinafter referred to as "(a,b) unit") may be alternatively repeated. Also, an (a,a,b) unit may be repeated.

The composite prepreg of the present invention can be obtained by conventional methods. For example, as shown in FIG. 4, fiber strands which are wound around two rolls 27 are dipped in a thermosetting resin bath 28 and then wound on a drum 26 with certain regularity. The thermosetting resin may be one well known in the art, but includes epoxy resins.

The composite prepreg of the present invention has suitable toughness for tennis rackets. A conventional prepreg in which only aromatic polyamides or polyester fibers are embedded is too tough to be drilled through, but the prepreg of the present invention is not so tough in comparison thereto. The prepreg of the present invention has physical properties somewhere between the conventional polyamide or polyester prepreg and a convention carbon prepreg.

The frame or shaft for the tennis rackets of the present invention is generally prepared by winding one or more prepregs around a core and then heating in a mold. All prepregs may be those of the present invention, but preferably some of them are those of the present invention and the other prepregs are the conventional carbon fiber, polyamide fiber, polyester fiber, boron fiber, carbon silicate fiber, or glass fiber prepregs. The number of the prepregs is not limited, but preferably 4 to 8 prepregs in which at least one, preferably 2 to 4 are more preferably the prepregs of the present invention.

The obtained tennis racket is light and tough and suitable in flexibility and vibration absorption, but still is easy to drill through the frame for stringing the gut.

EXAMPLES

The present invention is illustrated by the following Examples which, however, are not to be construed as limiting the scope of the present invention.

Examples 1 to 4 and Comparative Examples 1 to 6 Preparation of Prepregs

A composite prepreg C+A was prepared using an apparatus of FIG. 4 from thermosetting resin (epoxy resin Dow 331 available from Dow Chemical Co., Ltd.), polyamide fiber strands (Kevler 49, strand diameter=7,500 denier; available from Toray Dupont Co., Ltd) and carbon fiber strands (Besfight HTA strand diameter=7,200 denier, available from Toho Rayon Co., Ltd.). The carbon fiber strands and the polyamide fiber strands are alternatively arranged.

A composite prepreg C+E was prepared as mentioned above, with the exception that polyester fiber strands (Vektran, strand diameter=7,500 denier, available from Kuraray Co., Ltd.) was employed instead of the polyamide fiber strands.

A glass fiber prepreg G was prepared as generally described above, with the exception that only glass fiber strands ER 1150 (strand diameter=10500 denier, available from Nihon Ita Glass Co., Ltd.) were employed.

A carbon fiber prepreg C was also prepared as generally described above, with the exception that only carbon fiber strands as described.

A polyamide fiber prepreg A was prepared as desired above, with the exception that only the polyamide fiber strands were employed.

A polyester fiber prepreg E was prepared as described above, with the exception that only the polyester fiber strands were employed.

Preparation of Tennis Rackets

A core was wound with five prepregs and heated at 160 C. for 5 minutes in a mold to form a frame and a shaft. FIG. 1 schematically shows a section of the five prepregs layers. The prepregs used are listed in Table 1. A tennis racket was formed from the obtained frame and shaft and subjected to the evaluation of frame strength and vibration absorption. The results of the evaluation are shown in Table 1.

The frame strength was determined by simultaneously pressing the frame of a tennis racket from the directions shown in FIG. 2 until the frame was destroyed. Frame strength is expressed as a load (Kg) when the frame was destroyed.

The vibration absorption utilizing vibrator 2 was calculated from the following equation: ##EQU1## It was carried out using a system as shown in FIG. 3.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

                                  TABLE 1__________________________________________________________________________       Examples        Comparative Examples       1   2   3   4   1  2  3  4__________________________________________________________________________First layer G   G   G   G   G  G  G  GSecond layer       C   C   C + A                   C + E                       A  E  A  EThird layer C + A           C + E               C + A                   C + E                       C  C  A  EForth layer C + A           G + E               C + A                   C + E                       C  C  C  CFifth layer C   C   C + A                   C + E                       C  C  C  CTotal weight of a racket       330 330 310 310 330                          330                             310                                310Frame strength (Kg)       145 150 122 125 108                          110                             87 85Vibration absorption       42  38  25  22  49 45 36 31__________________________________________________________________________
Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4429873 *Aug 12, 1981Feb 7, 1984Snauwaert En Depla N.V.Tennis racket
US4532275 *Jan 29, 1982Jul 30, 1985Teijin LimitedFiber-reinforced composite materials
GB2217641A * Title not available
JPH01174413A * Title not available
JPS6259030A * Title not available
JPS58205755A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5700210 *Apr 10, 1996Dec 23, 1997Yamaha CorporationRacket frame and process for producing the same
US7790637Oct 31, 2007Sep 7, 2010Apple Inc.plurality of sheets of prepreg stacked one over another, each sheet including fibers preimpregnated with resin; scrim layer provided on exterior surface of sheets of prepreg, wherein scrim layer and sheets of prepreg form composite laminate; scrim layer made of nonwoven mat of randomly oriented fibers
US8562886Sep 3, 2010Oct 22, 2013Apple Inc.Composite laminate having an improved cosmetic surface and method of making same
Classifications
U.S. Classification428/374, 273/DIG.23, 428/902, 428/413, 473/521, 428/36.1, 473/535, 428/36.3
International ClassificationA63B49/10, A63B59/00, A63B49/02, B29C70/08, B29C70/86
Cooperative ClassificationB29K2307/00, B29C70/08, Y10S428/902, A63B2049/0252, A63B49/10, B29K2267/00, Y10S273/23, A63B2209/023, A63B59/0074, A63B59/0092, B29C70/865, B29K2277/00
European ClassificationB29C70/08, A63B49/10, B29C70/86A
Legal Events
DateCodeEventDescription
Jun 15, 2007FPAYFee payment
Year of fee payment: 12
May 16, 2005ASAssignment
Owner name: SRI SPORTS LIMITED, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SUMITOMO RUBBER INDUSTRIES, LTD.;REEL/FRAME:016561/0471
Effective date: 20050511
Owner name: SRI SPORTS LIMITED,JAPAN
Jun 17, 2003FPAYFee payment
Year of fee payment: 8
Jun 28, 1999FPAYFee payment
Year of fee payment: 4